2012 Costa Rica earthquake
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| Date | September 5, 2012 |
|---|---|
| Magnitude | 7.6 Mw |
| Depth | 40.2 km (25.0 mi) |
| Epicenter | 9°59′46″N 85°19′05″W / 9.996°N 85.318°W |
| Areas affected | Costa Rica |
| Max. intensity | X (Extreme) |
| Peak acceleration | 1.61 g (1580.0 cm/s2) |
| Aftershocks | 1,650 |
| Casualties | 2 |
The 2012 Costa Rica earthquake occurred at 08:42 local time (14:42 UTC) on September 5. The epicenter of the 7.6 Mw earthquake was in the Nicoya Peninsula, 11 kilometers east-southeast of Nicoya. A tsunami warning was issued shortly afterwards, but later cancelled. Two people are known to have died, one from a heart attack and another, a construction worker, crushed by a collapsing wall. It was the second strongest earthquake recorded in Costa Rica's history, following the 1991 Limon earthquake.
Costa Rica lies above the convergent plate boundary where the Cocos Plate is subducting beneath the Caribbean Plate at a rate of 9 cm per year. Off the Nicoya Peninsula, the Cocos Plate is subducting along the Middle America Trench, and the Nicoya Peninsula is unique in being one of the few landmasses along the Pacific Rim located directly above the seismogenic zone of a subduction megathrust fault. The earthquake is thought to have occurred as a result of thrust faulting on the plate interface. The earthquake has a maximum slip of about 2.5 m. The 1950 earthquake essentially the same part of the plate boundary as the 2012 earthquake.
The same area was struck by a M7.7 earthquake in 1950 but had been quiet before the recent earthquake, and the segment of the plate boundary was known as the Nicoya Peninsula seismic gap. In the intervening period, up to 2010, there was an estimated 5 m of missing displacement. Studies determined that the earthquake recurrence interval for the Nicoya Peninsula was about 50 years. The Volcanological and Seismological Observatory of Costa Rica (OVSICORI) stated that the earthquake had released 40% of the energy accumulated during the 8 years before it and did not exclude the possibility of an earthquake of equal or larger magnitude.
The earthquake was felt all over Costa Rica as well as in Nicaragua, El Salvador, and Panama. The maximum intensity reached MM X or higher in Nosara near the epicenter. The shaking has intensities of MM VIII in Santa Cruz and MM V in San José. The recorded acceleration in Fraijanes, Alajuela was larger than that of Nicoya, Guanacaste. A tsunami warning was issued for neighbouring countries along the Pacific Coast shortly afterwards, but later cancelled.
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